1. Field of the Invention
The present invention relates to a stationary blade (or stator blade) provided in gas turbines and a gas turbine comprising the same.
2. Description of the Related Art
As shown in FIG. 4, a gas turbine 10 has the following major constituents: (i) a compressor (not shown) for compressing air for combustion and supplying the compressed air to a combustor 20, (ii) the combustor 20 for injecting fuel into the air supplied from the compressor so as to burn the air and produce high-temperature combustion gas G, and (iii) a turbine portion 30 which is positioned at the downstream side of the combustor 20 and is driven by the combustion gas G transferred from the combustor 20.
As a typical example, the turbine portion 30 has a first-row stationary blade 31, a first-row moving blade (or rotor blade) 32, a second-row stationary blade 33, a second-row moving blade 34, a third-row stationary blade 35, a third-row moving blade 36, a fourth-row stationary blade 37, and a fourth-row moving blade 38.
The first-row stationary blade 31 has an outer shroud 31a, a main body 31b whose cross-section has a wing-section shape, and an inner shroud 31c. The first-row stationary blade 31 is fastened in a chamber (not shown) at the stator side via the outer shroud 31a. Similarly, the second-row stationary blade 33 has an outer shroud 33a, a main body 33b whose cross-section also has a wing-section shape, and an inner shroud 33c. The second-row stationary blade 33 is fastened in the chamber at the stator side via the outer shroud 33a. Also similarly, the third-row stationary blade 35 has an outer shroud 35a, a main body 35b whose cross-section also has a wing-section shape, and an inner shroud 35c. The third-row stationary blade 35 is fastened in the chamber at the stator side via the outer shroud 35a. Also similarly, the fourth-row stationary blade 37 has an outer shroud 37a, a main body 37b whose cross-section also has a wing-section shape, and an inner shroud 37c. The fourth-row stationary blade 37 is fastened in the chamber at the stator side via the outer shroud 37a. 
These first-, second-, third-, and fourth-row stationary blades are provided for expanding and decompressing the combustion gas G and directing the gas blown from the stationary blades so that the gas can collide with the moving blades 32, 34, 36, and 38 (which are positioned at the downstream side) at an optimum angle.
The first, second, third, and fourth moving blades 32, 34, 36, and 38 respectively have main bodies 32b, 34b, 36b, and 38b, and platforms 32d, 34d, 36d, and 38d are respectively attached to the base ends of these main bodies 32b, 34b, 36b, and 38b. The moving blades 32, 34, 36, and 38 are respectively attached via these platforms to moving blade disks 32e, 34e, 36e, and 38e. 
The flow of the combustion gas G will be explained below. The combustion gas G, which has a high temperature due to the combustion in the combustor 20, is drawn from the first-row stationary blade 31 and expands while flowing through the second to fourth stationary blades, thereby rotating the moving blades 32, 34, 36, and 38 and providing rotational power to a turbine rotor. The combustion gas G is then discharged.
FIG. 5 is an enlarged view of the portion surrounded by circle A′ in FIG.4. In FIG. 5, a heat insulating material 39, which may be a honeycomb seal made of porous ceramic, is provided at a rear-edge vicinity portion 33f of the inner shroud 33c (i.e., a portion in the vicinity of the rear edge of the inner shroud 33c) and on an inner-peripheral face 33g along which cooling air C passes and which faces a rotation shaft R (see FIG. 4) of the moving blade disks.
However, in this structure having the heat insulating material 39 at the rear-edge vicinity portion 33f of the inner shroud 33c, the inner-peripheral face 33g does not thermally communicate with the cooling air C; thus, heat of the rear-edge vicinity portion 33f of the inner shroud 33c is not sufficiently removed by the cooling air C, thereby producing thermal stress at this portion.